This invention relates to controller devices for vehicle automatic transmissions including oil-pressure driven type friction elements for engaging and disengaging the speed change gears of the transmission to realize desired gear ratios, and more particularly this invention relates to electronic control devices for controlling the electric oil pressure converter valves to regulate the oil pressures supplied to the oil-pressure driven type friction elements to engage and disengage the speed change gears.
A conventional controller device for vehicle automatic transmission by which the oil pressures of the friction elements of the transmission are controlled by means of electric oil pressure converter valves (solenoid valves) is disclosed, for example, in Japanese Laid-Open Patent (Kokai) Nos. 3-163265 and 1-27301. The transmission is capable of realizing a plurality of forward gear ratios, and electric oil pressure converter valves are inserted in the oil lines communicating the oil-pressure driven type friction elements and the manual valves. The oil pressures supplied to the oil-pressure driven type friction elements are directly controlled by means of the electric oil pressure converter valves. The time at which the friction elements corresponding to the desired gear ratio begin to engage (the actual start time of the gear shifting operation) is determined on the basis of the amount of the variation of the rotational speed of the input shaft to the transmission. The operating oil pressures of the friction elements are controlled from this start time of the gear shift.
The above conventional controller device for vehicle automatic transmission, however, has the following disadvantage. The oil-pressure driven type friction elements are controlled to perform the gear shift, wherein the start and the end of the gear shifting operation are determined on the basis of (the variations of) the rotational speed of the input shaft to the transmission. However, due to the variation in the production characteristics of the friction elements or the variation in the operating oil pressures, the engagements of the friction elements for realizing the desired gear ratio may be insufficient, such that the variation in the rotational speed of the input shaft to the transmission may not rise to a predetermined reference level. Then, the start of the gear shift cannot be determined, and hence the gear shifting operation is continued indefinitely to cause excessive slips of the friction elements. This not only results in an uneconomical loss of motive power, but also in rapid and premature abrasion of the friction elements.